It has been almost 40 years since Birute Galdikas established her study site for primates, deep in the heart of Tanjung Puting National Park in Kalimantan, Indonesian Borneo. Here, she used to stand waist-deep in swampy forest water, neck craning and eyes straining upwards to record every single move the orangutans she was observing made. Every night she would return to her pondok, a small wooden shelter, collate information, and pluck off stray leeches that had crept under her clothing, unnoticed during the course of the day.

Orangutans were unknown entities when her studies commenced in 1971. There were no roads, electricity, telephones or even a mail service in Borneo at that time. Initially set up to document orangutans in the wild, Camp Leakey served as a rehabilitation site for ex-captive orangutans, as the forests they were surrounded by started to dwindle. Eventually, Birute Galdikas was recognised as the foremost authority on these auburn-coloured primates, and Camp Leakey became inundated with orangutan orphans, illegally kept as pets before the owners found them too difficult to handle.

Now, the site is open to tourists and it is the closest any of us will come to experiencing these animals in the wild. It is best to arrange your tour through one of the travel agencies in Pangkalan Bun such as Borneo Holidays (www.borneowisata.com), which takes the hassle out of choosing a boat, captain, guide and a cook. If you arrive in the port town of Kumai first, the boats to look out for are the well-maintained Kingfisher and Garuda.

The trip to Camp Leakey takes two days on one of these boats. Named a klotok, this is a quaint wooden Indonesian houseboat that comfortably sleeps four people. It is an unforgettable, magical journey, where you are cut off from the rest of the world and thrust into what little nature remains of this vast tropical island. This is, importantly, one of the last remaining refuges for orangutans in the wild.

A guide is necessary for entering the national park. Armed with information, they will be able to explain to you the plight of the orangutans. They are also excellent wildlife spotters, and if you come face to face with a full grown male they will tell you what to do. Most of the guides have been working in the forest for years and have insider information into each of the individual orangutans around the Camp Leakey site. They will also be able to tell the difference between an ex-captive orangutan and a wild one.

During the quieter parts of the year (avoid August where increased numbers of tourists scatter the wildlife away from the river, and fruiting season drives the orangutans deep into the forest), you will not need to travel far before you see trees filled with proboscis monkeys. When you turn into the Sekonyer River, closer towards Camp Leakey, the river becomes narrow and you will get a great view of the male monkey's enormous snout - which is so big they have to move them out of the way to eat.

Silver leaf monkeys and troupes of macaques are also common sightings in this forest. Hornbills swoop before the klotoks, disturbed by the occasional passing speedboat taking workers to the nearby goldmine. On the way to Camp Leakey, two stops are made at feeding sites for rehabilitated and wild orangutans at Pondok Tanggui and Tanjung Harapan. The feeding platform is not far into the jungle, where birds chatter, mosquitoes hum and cicadas buzz like chainsaws, and there is an expectant quiet as the guides call for the orangutans, who eventually come crashing through the forest. Dominant males with massive cheek pads sit on the feeding platform and scoff bananas for an hour. Mothers and babies comically stuff fruit into their mouths, hands and feet before fleeing into the forest.

Visitors interested in the conservation efforts being made in the National Park can enter the tiny Sekonyer in the heart of the national park, where a library has been set up to educate the local children. Yayorin (www.yayorin.org) is an Indonesian-based conservation project with the mammoth task of teaching its people about conserving the forest and its creatures, with the chief aim being saving existing populations of orangutans.

As your klotok arrives at the long jetty at Camp Leakey, you will usually see several of the site's more famous characters lurking at the docking station. Siswi, an oversized female, is the offspring of one of Galidikas' original ex-captives. Tutut is another regular, who has become famous more recently for giving birth to a rare set of twins. Clever Princess was successfully taught how to use sign language, and was also nearly very successful staging her own escape attempt via a docked canoe. The one orangutan you really do not want to be lying in wait when the boats to arrive is Tom, the dominant male, once spotted angrily pulling the wooden bench from the jetty's shelter and hurling it into the river. And this is when your guide will come in handy. They can also shoo away one of the many macaques that are not too shy to steal food directly from the landing klotoks.

Gibbons also call these forests home, and every morning before sunrise you will be woken up to their songs. There is a special species of Bornean gibbon here, and you will get to see some of them up close. These gibbons are not scared of people and will brachiate at full speed over your awestruck head. Watching acrobatic gibbons at play is endlessly entertaining; just keep a firm grip on your camera.

At the site is an information centre which contains a fascinating insight into Galdikas' history at Camp Leaky, including the National Geographic feature she wrote that catapulted her and her primates to an international level in 1975. Learn about the generations of orangutans who have passed through this camp, as well as other forest creatures. Do not miss the documentary Kusasi, From Orphan to King, about the campsite's most famous inhabitant. However interesting all these features are, the best part of Camp Leakey is the once-in-a-lifetime opportunity to sit in a forest and share space with these semi-wild orangutans.

You can also go bushwalking on one of the many trails in the surrounding forests - just watch out for leeches. There are still things to look forward to along the way back: proboscis monkeys, kingfishers, hornbills and crocodiles. Plus, you should also not be surprised to see wild orangutans lurking on the riverbanks, or idly watching klotoks pass from the forest canopy. Toward the end of the journey, the forest shrinks and is gradually replaced by tall reeds. When night falls, thousands of fireflies light up these river reeds like Christmas trees, making this a truly fairytale end to a very special journey.